1. Field of the Invention
The present invention relates generally to methods and apparatus for the detection and treatment of sleep disorder breathing. More particularly, the present invention relates to methods and apparatus for detection and treatment of sleep disorder breathing that employ artificial neural networks.
2. Background Information
Disorders of excessive sleepiness present particular health-care concerns. Patients suffering from these disorders experience drowsiness and the need or desire to take naps during the day, and such patients present a history of divorces, employment problems, and automotive accidents.
Among the most common types of sleep disorder breathing is sleep apnea, in which patients experience a partial or complete interruption of air flowing into the lungs for periods exceeding ten seconds. Between 1 and 15 percent of the population is believed to suffer from this condition. Sleep apnea can cause repeated disruption or even cessation of rapid eye movement (REM) sleep, which can cause irritability and a reduction in the ability to memorize information.
There are three recognized types of sleep apnea. Central sleep apnea is characterized by the suspension of all respiratory movement and is generally believed to be neurological in origin. Obstructive sleep apnea is characterized by the collapse of the upper airways during sleep. The third type of sleep apnea is a combination of central and obstructive sleep apnea and is known as mixed apnea.
Obstructive sleep apnea appears to be the most common form of sleep apnea and occurs when the upper respiratory airway of the patient collapses because the tonal activity of the pharyngeal smooth muscle fails to maintain the patency of the airway. Although sporadic and brief airway collapses or obstructive events are not uncommon in the normal adult population, it is considered pathological when obstructive apnea episodes last more than ten seconds and occur over seven-to-ten times per hour.
A symptom indicative of the onset of obstructive sleep apnea is pharyngeal wall vibration, commonly known as snoring. Early detection of pharyngeal wall vibration, and prophylactic treatment of the condition can lead to successful treatment of obstructive sleep apnea. Surgical treatments of obstructive sleep apnea are successful when anatomical abnormalities appear to be the principal cause of obstructive sleep apnea. Non-surgical treatments are successful as well.
One successful non-surgical treatment method is the use of continuous positive airway pressure (CPAP) apparatus. CPAP apparatus administers air or respiratory gas to the patient's airways at a slightly positive pressure level (5 to 20 cmH.sub.2 O), which maintains the patency of the respiratory airways. The pressure exerted by CPAP apparatus is believed to act as a pneumatic splint for the upper airway. The low-level pressure of the CPAP apparatus is selected after study of the patient in a sleep laboratory. The selected maximum pressure from the sleep study is referred to as prescribed CPAP pressure. Although CPAP apparatus is an effective treatment in 75% of treated patients, the positive airway pressure delivered throughout sleep can cause patient discomfort, including airway pain and dehydration.
An improvement upon CPAP apparatus is described in U.S. Pat. No. 5,458,137, Oct. 17, 1995, to Axe et al., and is known as Adaptive Positive Airway Pressure (APAP) apparatus. APAP apparatus works on the same principle as CPAP apparatus, but does not deliver a single prescribed CPAP pressure. The positive airway pressure administered by APAP is adjusted according to the current needs of the patient, based upon an analysis of the patient's breathing patterns. Principally, if pharyngeal wall vibration is detected, the pressure is increased incrementally. If the patient breathes normally, pressure is decreased. Use of APAP apparatus alleviates some of the patient discomforts with high prescribed CPAP pressures. The ability of APAP apparatus to deliver adequate pressure to the patient is based upon its ability to detect pharyngeal wall vibration or apneic events accurately.
A need exists, therefore, for methods and apparatus for the treatment of sleep disorder breathing that employs detection apparatus having improved ability to detect pharyngeal wall vibration or other apneic events accurately.